# How to find the QRS complex for this ECG signal?

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Susan on 8 Dec 2022
Commented: Susan on 13 Dec 2022
Hi all,
Could somebody please tell me how I can find the QRS complexes of this ECG signal? The signal is attached.
William Rose on 13 Dec 2022
@Susan, you're welcome. Good luck with your work.

William Rose on 13 Dec 2022
ECG=ECGs.ECG;
L = numel(ECG);
t = linspace(0, L-1, L)/1024;
[pks,locs] = findpeaks(ECG,'MinPeakDistance',2,'MinPeakHeight',max(ECG)*0.6846);
%[pks,locs] = findpeaks(ECG,'MinPeakDistance',2,'MinPeakHeight',.48);
figure
subplot(311), plot(t, ECG, '-r',t(locs), pks, '^r')
xlabel('Time (s)'); grid on
subplot(312), plot(t, ECG, 'r-',t(locs), pks, '^k')
xlim([0 5]); xlabel('Time (s)'); grid on
subplot(313), plot(t, ECG, '.r-',t(locs), pks, '^k')
xlim([4 5]); xlabel('Time (s)'); grid on
The 10 Hz spikes are a bit narrower than the QRS complexes, so it should be possible to identify the QRS complexes based on that, plus the peak height excedigng approximately 0.4. This should allow you to find all of the R waves.
Was the subject paced? The R-R intervals appear to be too even for unpaced beats.
Good luck.
Susan on 13 Dec 2022
@William Rose Sure thing!